Question: $ \left(\dfrac{16}{81}\right)^{-\frac{1}{2}}$
Explanation: $= \left(\dfrac{81}{16}\right)^{\frac{1}{2}}$ Figure out what goes in the blank: $\Big(? \Big)^{2}=\dfrac{81}{16}$ Figure out what goes in the blank: $\Big({\dfrac{9}{4}}\Big)^{2}=\dfrac{81}{16}$ So $\left(\dfrac{16}{81}\right)^{-\frac{1}{2}}=\left(\dfrac{81}{16}\right)^{\frac{1}{2}}=\dfrac{9}{4}$